Sure thing, let's get straight to it. We start with 816 and we're going to multiply it by 123, which means adding 816 to itself 123 times.
Step 1: 0 + 816 = 816
Step 2: 816 + 816 = 1632
Step 3: 1632 + 816 = 2448
Step 4: 2448 + 816 = 3264
Step 5: 3264 + 816 = 4080
Step 6: 4080 + 816 = 4896
Step 7: 4896 + 816 = 5712
Step 8: 5712 + 816 = 6528
Step 9: 6528 + 816 = 7344
Step 10: 7344 + 816 = 8160
Step 11: 8160 + 816 = 8976
Step 12: 8976 + 816 = 9792
Step 13: 9792 + 816 = 10608
Step 14: 10608 + 816 = 11424
Step 15: 11424 + 816 = 12240
Step 16: 12240 + 816 = 13056
Step 17: 13056 + 816 = 13872
Step 18: 13872 + 816 = 14688
Step 19: 14688 + 816 = 15504
Step 20: 15504 + 816 = 16320
Step 21: 16320 + 816 = 17136
Step 22: 17136 + 816 = 17952
Step 23: 17952 + 816 = 18768
Step 24: 18768 + 816 = 19584
Step 25: 19584 + 816 = 20400
Step 26: 20400 + 816 = 21216
Step 27: 21216 + 816 = 22032
Step 28: 22032 + 816 = 22848
Step 29: 22848 + 816 = 23664
Step 30: 23664 + 816 = 24480
Step 31: 24480 + 816 = 25296
Step 32: 25296 + 816 = 26112
Step 33: 26112 + 816 = 26928
Step 34: 26928 + 816 = 27744
Step 35: 27744 + 816 = 28560
Step 36: 28560 + 816 = 29376
Step 37: 29376 + 816 = 30192
Step 38: 30192 + 816 = 31008
Step 39: 31008 + 816 = 31824
Step 40: 31824 + 816 = 32640
Step 41: 32640 + 816 = 33456
Step 42: 33456 + 816 = 34272
Step 43: 34272 + 816 = 35088
Step 44: 35088 + 816 = 35904
Step 45: 35904 + 816 = 36720
Step 46: 36720 + 816 = 37536
Step 47: 37536 + 816 = 38352
Step 48: 38352 + 816 = 39168
Step 49: 39168 + 816 = 39984
Step 50: 39984 + 816 = 40800
Step 51: 40800 + 816 = 41616
Step 52: 41616 + 816 = 42432
Step 53: 42432 + 816 = 43248
Step 54: 43248 + 816 = 44064
Step 55: 44064 + 816 = 44880
Step 56: 44880 + 816 = 45696
Step 57: 45696 + 816 = 46512
Step 58: 46512 + 816 = 47328
Step 59: 47328 + 816 = 48144
Step 60: 48144 + 816 = 48960
Step 61: 48960 + 816 = 49776
Step 62: 49776 + 816 = 50592
Step 63: 50592 + 816 = 51408
Step 64: 51408 + 816 = 52224
Step 65: 52224 + 816 = 53040
Step 66: 53040 + 816 = 53856
Step 67: 53856 + 816 = 54672
Step 68: 54672 + 816 = 55488
Step 69: 55488 + 816 = 56304
Step 70: 56304 + 816 = 57120
Step 71: 57120 + 816 = 57936
Step 72: 57936 + 816 = 58752
Step 73: 58752 + 816 = 59568
Step 74: 59568 + 816 = 60384
Step 75: 60384 + 816 = 61200
Step 76: 61200 + 816 = 62016
Step 77: 62016 + 816 = 62832
Step 78: 62832 + 816 = 63648
Step 79: 63648 + 816 = 64464
Step 80: 64464 + 816 = 65280
Step 81: 65280 + 816 = 66096
Step 82: 66096 + 816 = 66912
Step 83: 66912 + 816 = 67728
Step 84: 67728 + 816 = 68544
Step 85: 68544 + 816 = 69360
Step 86: 69360 + 816 = 70176
Step 87: 70176 + 816 = 70992
Step 88: 70992 + 816 = 71808
Step 89: 71808 + 816 = 72624
Step 90: 72624 + 816 = 73440
Step 91: 73440 + 816 = 74256
Step 92: 74256 + 816 = 75072
Step 93: 75072 + 816 = 75888
Step 94: 75888 + 816 = 76704
Step 95: 76704 + 816 = 77520
Step 96: 77520 + 816 = 78336
Step 97: 78336 + 816 = 79152
Step 98: 79152 + 816 = 79968
Step 99: 79968 + 816 = 80784
Step 100: 80784 + 816 = 81600
Step 101: 81600 + 816 = 82416
Step 102: 82416 + 816 = 83232
Step 103: 83232 + 816 = 84048
Step 104: 84048 + 816 = 84864
Step 105: 84864 + 816 = 85680
Step 106: 85680 + 816 = 86496
Step 107: 86496 + 816 = 87312
Step 108: 87312 + 816 = 88128
Step 109: 88128 + 816 = 88944
Step 110: 88944 + 816 = 89760
Step 111: 89760 + 816 = 90576
Step 112: 90576 + 816 = 91392
Step 113: 91392 + 816 = 92208
Step 114: 92208 + 816 = 93024
Step 115: 93024 + 816 = 93840
Step 116: 93840 + 816 = 94656
Step 117: 94656 + 816 = 95472
Step 118: 95472 + 816 = 96288
Step 119: 96288 + 816 = 97104
Step 120: 97104 + 816 = 97920
Step 121: 97920 + 816 = 98736
Step 122: 98736 + 816 = 99552
Step 123: 99552 + 816 = 100368

So, 816*123 = 100368